Study On The Growth,cadmium Accumulation And Rhizosphere Bacterial Community Structure Of Four Maize Varieties In Lead-zinc Mining Area

Yunnan is rich in lead,zinc and other mineral resources,and long-term mining and smelting activities lead to serious heavy metal pollution such as cadmium（Cd）and lead（Pb）in the soil around the mining area.Maize is one of the main crops planted around the mining area,and its accumulation of heavy metals is closely related to the root character.However,there are few studies on the cumulative characteristics and root traits of Cd and Pb of different maize varieties in the polluted farmland around the lead-zinc mining area in Yunnan Plateau.Four Cd high and low accumulation（Panyu 3 with Cd,Zhou Yu 0913,Cd low order 16 and Enyu 98）used a field experiment in the lead-zinc mining area in Yunnan province to study the root characteristics and Cd and Pb accumulation characteristics and the effects of Cd and Pb accumulation.The results are as follows:（1）There were obvious variety differences in maize root morphology and configuration in field experiments.The difference in root morphology（root length,root surface area,average root diameter,root tip number,root volume and branch number）of the four maize varieties could reach 1.8-4.1 times,and the difference in root configuration（root length,root density,root tip,and root branch）was 1.5-1.9times.（2）The largest root Cd was Panyu No.3(978.9μg plant^-1)and the minimum was roadside 16(257.3μg plant^-1)by 3.8 times;the largest root Pb was Panyu 3(415.7μg plant^-1)and the lowest was roadside 16(only 93.5μg plant^-1),with a difference of 4.4times.In addition,the distribution of Cd and Pb in maize was root>leaves>stem>grains.And the plant Cd accumulation,root and stem Pb accumulation and root length,root surface area,average root diameter,root tip,root volume and branches,leaf Pb accumulation and root length,root surface area,root diameter,stem Cd accumulation than root length,grain Pb content and root mass density（pole）significant positive correlation,indicating that maize Cd and Pb accumulation characteristics is closely related to root morphology and root structure traits.（3）Differences in the rhizosphere microbial communities among maize varieties.At the phylum level,the bacterial microbial communities of the rhizosphere were dominated by proteobacteria（Proteobacteria,28.45%～37.78%）and Acidobacteria（Acidobacteria,10.55%～18.54%）.At the genus level,rhoanella（Rhodanobacter,20.78%～48.06%）was the largest proportion.According to LEf Se analysis,the four varieties of maize rhizosphere had significantly different microbial groups,including21 species in Lushan 16,9 species in Panyu 3,13 species in Zhou Yu 0913 and 4species in Enyu 98.Through NMDS analysis,it was found that although the rhizosphere of maize varied,there were some similarities（stress=0.099<0.1,P<0.05）.（4）Redundancy（RDA）analysis of the physicochemical properties of soil in the rhizosphere found that the axes explained 33.71%of the variation in bacterial genus level.The effect of soil physiochemical properties on jointing maize rhizosphere microbial communities（P>0.05）,However,p H,TP,Cd,and Pb were more correlated with the microbial community,TP and Pb content were positively correlated with the abundance of Bryobacter and Rhodanobacter,A negative correlation with Nitrospira and Gemmatimonas abundance;The Cd content was positively correlated with the abundance of Flavobacterium,Rhodanobacter,Sphingomonas,and Massilia.（5）Using the mature field maize rhizosphere soil as the inoculum,Conduct reciprocal transplant pot experiments of rhizosphere microorganisms,It was found that the root surface area,root volume of no.3 root sphere and branch number increased by 36.0-88.2%;The inoculation of Zhou Yu 0913 rhizosphere microorganisms caused a significant decrease in the mean root diameter,root volume and branch number of Enyu 98 by 14.3%-30.7%,Moreover,the aboveground Cd content and accumulation amount significantly increased by 125.9%and 135.3%,respectively,The Pb content and accumulation amount increased by 75.6%and 77.9%respectively;The inoculation of Enyu 98 rhizosphere microorganisms caused a significant reduction of 47.4%in the underground Cd accumulation of Zhou Yu 0913,The underground Pb content and the cumulative amount were significantly reduced by 23.2%and 51.8%,respectively.Showed that inoculation of rhizosphere microorganisms with relatively high cumulative varieties would result in improved root morphology,Cd and Pb cumulative ability of low cumulative varieties.（6）Structural equation model analysis showed that,Maize root traits and bacterial community structure had direct and indirect effects on root Cd and Pb accumulation,Root length,root Ca content,and specific root Cd accumulation were significantly directly affected（P<0.01）,Their path coefficient with root Cd were0.846,0.314,-0.393,respectively,The larger the path system value is,The greater the correlation between the two;in addition,The root length,root Cd accumulation and Shannon index had significant direct effects on root Pb accumulation（P<0.05）,Their accumulated path coefficients with the root Pb were 0.485,-0.403,0.662,and 0.239,respectively.In conclusion,the root traits of four varieties were obviously different from the cumulative traits of Cd and Pb,and their root morphology and configuration were positively correlated with Cd and Pb content and accumulation,and the rhizosphere microbial community structure could affect the Cd and Pb accumulation ability of maize,indicating the close relationship between root traits and rhizosphere microorganisms and Cd and Pb accumulation.